Vanackerite

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Vanackerite
General and classification
other names
  • IMA 2011-114
chemical formula
  • Pb 4 Cd [Cl | (AsO 4 ) 3 ]
  • Pb 4 Cd (AsO 4 ) 3 Cl
Mineral class
(and possibly department) 		Phosphates, arsenates, vanadates
Similar minerals Mimetite
Crystallographic Data
Crystal system trigonal
Crystal class ; symbol trigonal-pyramidal; 3
Space group P 3 (No. 147)Template: room group / 147
Lattice parameters a  = 10.0279  Å ; c  = 7.2965 Å
Formula units Z  = 2
Frequent crystal faces {0001}, {01 1 0}, {11 2 1} and {10 1 1}
Twinning no
Physical Properties
Mohs hardness VHS 25 = 270 kg / mm 2 , corresponds to a Mohs hardness of ≈ 4
Density (g / cm 3 ) 7.28 (calculated)
Cleavage not specified; not specified
Break ; Tenacity not specified
colour light yellow
Line color White
transparency translucent
shine Diamond luster
Crystal optics
Refractive index n  = 2.04 (calculated)
Optical character uniaxial
Other properties
Special features orange fluorescence under UV light (strongest at 366 nm)

Vanackerite is a very rarely occurring mineral from the mineral class of phosphates , arsenates and vanadates . It crystallizes in the trigonal crystal system with the chemical composition Pb 4 Cd [Cl | (AsO 4 ) 3 ], making it chemically seen a lead - cadmium - arsenate with additional chlorine ions .

Vanackerit develops pseudo-hexagonal, thin-tabular crystals that can come together to form rosette-shaped aggregates and are light yellow in color.

Etymology and history

The type specimen of Vanackerite was after its discovery in 1980 in an earlier collection of the former mineralogist of the Tsumeb Corporation John Innes, where it was for a long time mistaken for mimetesite. After it was acquired by Georg Gebhardt, he had the mimetite-like crystals examined, which after appropriate analyzes turned out to be a new mineral. The mineral was recognized by the International Mineralogical Association (IMA) in 2011 and described as vanackerite by Jochen Schlueter , Thomas Malcherek and Georg Gebhard in 2016 . It was named after the Belgian mineral collector Georges Vanacker (1923-1992), who built up an excellent systematic collection with many mineral specimens from the Tsumeb mine and donated it in 1991 to the Institut Royal des Sciences Naturelles de Belgique in Brussels , Belgium .

Type material of the mineral (holotype) is kept in the Mineralogical Museum of the University of Hamburg in Germany (catalog no. TS 706).

classification

Vanackerite was only recognized as an independent mineral by the International Mineralogical Association (IMA) in 2011 and the discovery was not published until 2016. A precise group assignment in the 9th edition of Strunz's mineral classification is therefore not yet known. If one follows the nomenclature of the apatite supergroup in the classification by Pasero et al. (2010), the vanackerite within the apatite supergroup can best be parallelized with the minerals of the Belovit group. This group currently only consists of phosphates - Vanackerite would be the first arsenate in this group. Among the representatives of the Belovit group, Vanackerite deviates most from the apatite structure type.

Since the mineral is a close relative of Belovit- (Ce) , Belovit- (La) and Kuannersuit- (Ce) , which due to their composition in the mineral class of "phosphates, arsenates and vanadates" and there in "With only large cations; (OH etc.): RO 4 = 0.33: 1 ” can be found, where they form the“ apatite group ”with numerous other minerals with the system no. Form 8.BN.05 , Vanackerit will probably also be sorted there.

Crystal structure

Vanackerite crystallizes in the trigonal crystal system in the space group P 3 (space group number 147) with the lattice parameters a  = 10.0279  Å and c  = 7.2965 Å as well as two formula units per unit cell . Template: room group / 147

The crystal structure of vanackerite can be derived from the hexagonal structure of the mimetite through the splitting of one of the Pb positions accompanied by a rotation of the arsenate tetrahedron , whereby cadmium atoms take over half of the P1 positions of the mimetite structure, which leads to an alternating arrangement of the Cadmium and lead atoms along [001] leads.

Chemism

Vanackerite has the measured composition Pb 4.10 Cd 0.98 As 2.92 O 12.07 Cl 0.61 . This formula can be written in simplified form as Pb 4 Cd (AsO 4 ) 3 Cl, which means a PbO content of 64.07%; 9.22% CdO; Requires 24.74% As 2 O 5 and 2.54% Cl. Vanackerite is another representative of the cadmium-containing minerals in Tsumeb; Of the 27 currently (2016) known cadmium minerals, five were found in Tsumeb. Four of these ( Otavit , Andyrobertsit , Keyit and Vanackerit) also have their type locality here. For Andyrobertsit and Vanackeit, Tsumeb is the only site in the world so far.

properties

morphology

According to {0001}, vanackerite forms thin-tabular, pseudo-hexagonal crystals up to 5 mm in diameter, which typically come together to form rosette-shaped aggregates. Their morphology is reminiscent of that of tabular to thin prismatic mimetite crystals. The main form is the basic pinacoid {0001}, {01 1 0}, {11 2 1} and {10 1 1} have been identified on other forms .

physical and chemical properties

The vanackerite crystals are light yellow, the line color of the mineral is described as white. The surfaces of the translucent crystals have a diamond-like sheen . The vanackerite shows a clear orange-colored fluorescence in long-wave UV light (maximum at 366 nm) . With a Mohs hardness of ≈ 4, Vanackerite is one of the medium-hard minerals that, like the reference mineral fluorite, can be easily scratched with a pocket knife. The calculated density of the mineral is 7.28 g / cm 3 .

Education and Locations

Vanackerite comes from the second (lower) oxidation zone of the hydrothermal polymetallic ore deposit Tsumeb, which is located in dolomite stones. Minerals accompanying the mineral are bluish green Thometzekit , Anglesit and gypsum .

So far (as of 2016) the mineral could only be found at its type locality . The type locality is the world-famous Cu-Pb-Zn-Ag-Ge-Cd deposit of the "Tsumeb Mine" (Tsumcorp Mine) in Tsumeb , Oshikoto region , Namibia . In addition, only one level of this mineral is known to date.

See also

literature

  • Jochen Schlüter, Thomas Malcherek, Georg Gebhard (2016): Vanackerite, a new lead cadmium arsenate of the apatite supergroup from Tsumeb, Namibia. In: New Yearbook Mineralogie Abhandlungen Volume 193 (Issue 1), pp. 79–86.

Web links

Individual evidence

  1. ↑ a b c d e f g h i j k l m n o p q Jochen Schlüter, Thomas Malcherek, Georg Gebhard (2016): Vanackerite, a new lead cadmium arsenate of the apatite supergroup from Tsumeb, Namibia. In: New Yearbook Mineralogie Abhandlungen , Volume 193 (Issue 1), pp. 79–86.
  2. ↑ Marco Pasero, Anthony R. Kampf, Christiano Ferraris, Igor V. Pekov, John R. Rakovan, Timothy J. White (2010): Nomenclature of the apatite supergroup minerals. In: European Journal of Mineralogy. , Volume 22, pp. 163–179 ( PDF 722.5 kB )
  3. ↑ Mindat - Number of localities for Vanackerite
  4. ↑ Find location list for Vanackerite in the Mineralienatlas and Mindat